U.S. patent number 7,234,358 [Application Number 11/354,959] was granted by the patent office on 2007-06-26 for pressure detecting apparatus.
This patent grant is currently assigned to Fuji Electric Device Technology Co., Ltd.. Invention is credited to Yuji Ichimura, Kazunori Saito, Shigeru Shinoda, Katsumichi Ueyanagi, Kei Yamaguchi.
United States Patent |
7,234,358 |
Saito , et al. |
June 26, 2007 |
**Please see images for:
( Certificate of Correction ) ** |
Pressure detecting apparatus
Abstract
A pressure detecting apparatus has a pressure detecting device
that converts a strain caused by a stress exerted thereto to an
electrical signal, and outputs the converted electrical signal. The
apparatus has a housing base including a housing recess that houses
the pressure detecting device therein, and a connecting material
interposed between the pressure detecting device and the housing
recess. The connecting material connects the pressure detecting
device and the housing recess with a tensile elongation percentage
of about 400% or higher. The pressure detecting apparatus
facilitates preventing thermal stress from adversely affecting the
detection performance thereof, and produces excellent thermal
response.
Inventors: |
Saito; Kazunori (Matsumoto,
JP), Ichimura; Yuji (Matsumoto, JP),
Yamaguchi; Kei (Matsumoto, JP), Ueyanagi;
Katsumichi (Matsumoto, JP), Shinoda; Shigeru
(Matsumoto, JP) |
Assignee: |
Fuji Electric Device Technology
Co., Ltd. (Tokyo, JP)
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Family
ID: |
37111646 |
Appl.
No.: |
11/354,959 |
Filed: |
February 16, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060243054 A1 |
Nov 2, 2006 |
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Foreign Application Priority Data
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Apr 27, 2005 [JP] |
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2005-130533 |
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Current U.S.
Class: |
73/754;
73/753 |
Current CPC
Class: |
G01L
19/0084 (20130101); G01L 19/146 (20130101); G01L
19/143 (20130101); G01L 19/147 (20130101); H01L
2224/48091 (20130101); H01L 2224/83385 (20130101); H01L
2924/15156 (20130101); H01L 2224/48091 (20130101); H01L
2924/00014 (20130101) |
Current International
Class: |
G01L
9/00 (20060101) |
Field of
Search: |
;73/700-756
;361/283.1-283.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2003-247903 |
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Sep 2003 |
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JP |
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2004-045184 |
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Feb 2004 |
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JP |
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WO 9400755 |
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Jan 1994 |
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WO |
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Primary Examiner: Lefkowitz; Edward
Assistant Examiner: Jenkins; Jermaine
Attorney, Agent or Firm: Kanesaka; Manabu
Claims
What is claimed is:
1. A pressure detecting apparatus comprising: a pressure detector
for converting a strain induced by a stress exerted thereto to an
electrical signal, and for outputting the electrical signal; a base
comprising a housing for accommodating the pressure detector
therein; and a connector, interposed between the pressure detector
and the housing, for connecting the pressure detector and the
housing, said connector having a tensile elongation percentage of
400% or higher.
2. The pressure detecting apparatus according to claim 1, wherein
the pressure detector comprises a semiconductor.
3. The pressure detecting apparatus according to claim 1, wherein
the base comprises a resin molding.
4. The pressure detecting apparatus according to claim 1, wherein
the connector comprises a silicone resin adhesive.
5. The pressure detecting apparatus according to claim 1, wherein
the connector is provided such that a distance between a bonding
plane of the pressure detector and a bonding plane of the housing
is from 30.mu.m to 100.mu.m.
6. The pressure detecting apparatus according to claim 1, wherein
said pressure detector comprises a pedestal, a semiconductor
substrate disposed on the pedestal, and a diaphragm attached to the
semiconductor substrate, said connector being arranged between
bottoms of the pedestal and housing of the base.
7. The pressure detecting apparatus according to claim 6, wherein
said base further includes a plurality of protrusions projecting
upwardly from the bottom of the housing to receive the pedestal
thereon.
8. The pressure detecting apparatus according to claim 7, further
comprising a protecting material for covering on and around the
pressure detector.
Description
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a pressure detecting apparatus
that converts the pressure detected thereby to an electrical signal
and outputs the converted electrical signal. Specifically, the
present invention relates also to a pressure detecting apparatus
that exhibits excellent thermal response.
Usually, the semiconductor pressure sensor chip that employs the
so-called piezoresistance effects has been used for a pressure
detecting apparatus for measuring the intake air pressure on the
air intake side of an engine in the electronic controlled fuel
injection apparatus for automobiles. Since the operational
principles of the pressure detecting apparatus that employs the
semiconductor pressure sensor chip as described above are well
known, the detailed descriptions thereof are omitted. The pressure
detecting apparatus includes a bridge circuit consisting of
semiconductor strain gauges formed on a diaphragm made of a
material that exhibits piezoresistance effects such as single
crystalline silicon. A pressure is detected by taking out the gauge
resistance changes, caused in the semiconductor strain gauges by
the diaphragm distortion, from the bridge circuit in the form of an
electrical signal.
Now the pressure detecting apparatus briefly described above will
be explained below with reference to FIGS. 5 and 6. FIG. 5 is a
cross-sectional view of a conventional pressure detecting
apparatus. FIG. 6 is an expanded cross-sectional view showing a
part of the conventional pressure detecting apparatus shown in FIG.
5. Referring now to these drawings, a pressure detecting apparatus
500 includes a pressure detecting device 501, that is a
semiconductor pressure sensor chip, mounted on a housing base 502
of a resin molding, that is a package casing of pressure detecting
apparatus 500. A housing recess 503 for housing pressure detecting
device 501 therein is formed in housing base 502.
Pressure detecting device 501 is mounted on housing base 502 in
such a configuration, in which pressure detecting device 501 is
bonded by die-bonding with an adhesive 504 to housing recess 503
formed in housing base 502. Pressure detecting device 501 is
electrically connected, via bonding wires 506, to lead terminals
(lead frames) 505 integrated into housing base 502 by insertion
molding such that lead terminals 505 are extending through housing
base 502.
For reducing the stress exerted from housing base 502 in the
structure described above, pressure detecting device 501 is bonded
to a pedestal 507 made of glass by the anodic bonding technique
known to those skilled in the art such that a vacuum reference
space is formed between pressure detecting device 501 and glass
pedestal 507. A gel protecting material 508 covers the surface 501a
of pressure detecting device 501 and adheres pressure detecting
device 501 to housing base 502 in such a manner that gel protecting
material 508 contains bonding wires 506 therein. Protecting
material 508 protects pressure detecting device 501 from the
contaminants contained in the not-shown medium, the pressure
thereof is to be measured with pressure detecting apparatus 500,
and transmits the medium pressure to pressure detecting device 501.
Protecting material 508 is also disposed between the side face of
detecting device 501 and the side face of housing recess 503.
A housing cover 510 formed of a molded resin material includes a
tube-shaped pressure transmitting section 509 having a cylindrical
inner surface 509a (cf. FIG. 5). Housing cover 510 is mounted on
and fixed, with an adhesive, to the opening side end portion of
housing recess 503 in housing base 502 such that a pressure
detecting space 511 consisting of a space connected to pressure
transmitting section 509 is formed (cf. FIG. 5). The medium
pressure to be measured is transmitted to pressure detecting space
511 through pressure transmitting section 509 in housing cover 510.
Pressure detecting apparatus 500 detects the pressure difference
between the transmitted medium pressure to be measured and the
vacuum reference room pressure as a pressure change, converts the
detected pressure change to an electrical signal in pressure
detecting device 501, and outputs the converted electrical signal.
Thus, the absolute medium pressure is measured.
For meeting the various demands for pressure detecting apparatus
500 such as down-sizing of entire pressure detecting apparatus 500,
realization of very precise detection characteristics and
realization of very high reliability, the opening size of housing
recess 503 is optimized so that a clearance optimum for reducing
the stress exerted from housing base 502 may be obtained between
pressure detecting device 501 and housing base 502 (cf. Japanese
Patent Publication No. 2003-247903).
In pressure detecting apparatus 500 having the structure as
described above, the deformation of housing base 502 caused by an
external stress exerted from housing cover 510 or by a thermal
stress due to a severe measurement environment associating drastic
temperature changes adversely affects the detection performances of
pressure detecting device 501, impairing the thermal response of
pressure detecting apparatus 500.
The thermal response is one of the evaluation items for
performances tests indicating the detection performances change
caused by the environmental temperature change, e.g. from a high
temperature to a low temperature. In the pressure detecting
apparatus, the thermal response thereof is not good, variations are
caused between the initial detection performances and the detection
performances after a temperature change is caused.
If the loading amount of adhesive 504 for mounting pressure
detecting device 501 on housing base 502 is too large, adhesive
504, which has bulged out of the gap between the bottom surface
503a of housing recess 503 and the bottom surface 507a of pedestal
507 creeps up the clearance between pressure detecting device 501
and housing base 502, that is, the gap between the side face 507b
of pedestal 507 and the side face 503b of housing recess 503 as
shown in FIG. 6. Therefore, the stress caused, for example, by the
deformation of housing base 502 in the direction indicated by the
outline arrows in FIG. 6 directly affects the detection
performances of pressure detecting device 501, impairing the
thermal response of pressure detecting apparatus 500.
In view of the foregoing, it would be desirable to provide a
pressure detecting apparatus that facilitates reducing the adverse
effects of thermal stress on the detection performances to the
extreme thereof and exhibits excellent thermal response.
Further objects and advantages of the invention will be apparent
from the following description of the invention and the associated
drawings.
SUMMARY OF THE INVENTION
According to one embodiment of the invention, there is provided a
pressure detecting apparatus including a pressure detecting means,
the pressure detecting means converting the strain caused by the
stress exerted thereto to an electrical signal, the pressure
detecting means outputting the converted electrical signal; a base
means including a housing means, the housing means housing the
pressure detecting means therein; and a connecting means interposed
between the pressure detecting means and the housing means, the
connecting means connecting the pressure detecting means and the
housing means at a tensile elongation percentage of 400% or
higher.
According to one aspect of the invention, the pressure detecting
means is made of a semiconductor.
According to another aspect of the invention, the base means is
formed of a resin molding.
According to another aspect of the invention, the connecting means
is made of a silicone resin adhesive.
According to another aspect of the invention, the connecting means
is formed such that the distance between the bonding plane of the
pressure detecting means and the bonding plane of the housing means
is from 30 .mu.m to 100 .mu.m.
Since the pressure detecting means and the base means are connected
and fixed to each other with the connecting means exhibiting an
elongation percentage of about 400% or higher, the pressure
detecting apparatus according to the invention that facilitates
absorbing the exerted stress based on the excellent elongation
characteristics exhibits excellent thermal response.
The pressure detecting apparatus according to the invention that
exhibits excellent thermal response facilitates realizing a
structure immune to temperature changes caused in the measurement
environment and obtaining measurement results with very high
reproducibility.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan view of a pressure detecting apparatus
according to a first embodiment of the invention.
FIG. 2 is a cross-sectional view along the line segment 2 2' in
FIG. 1.
FIG. 3A is an expanded cross-sectional view of a part of FIG.
2.
FIG. 3B is a cross-sectional view showing a modification of the
structure shown in FIG. 3A.
FIG. 4 shows a curve relating the output variation (%F.S..times.10)
caused by the thermal response shift with the tensile elongation
percentage (%) of the connecting material.
FIG. 5 is a cross-sectional view of a conventional pressure
detecting apparatus.
FIG. 6 is an expanded cross-sectional view showing a part of the
conventional pressure detecting apparatus shown in FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now the invention will be described in detail hereinafter with
reference to the accompanied drawings which illustrate the
preferred embodiments of the invention. In the descriptions of the
embodiments and the drawings illustrating the embodiments, the same
reference numbers are used to designate the same of like
constituent elements and their duplicated explanations are omitted
for the sake of simplicity.
FIG. 1 is a top plan view of a pressure detecting apparatus
according to a first embodiment of the invention. FIG. 2 is a
cross-sectional view along the line segment 2 2' in FIG. 1. FIG. 3A
is an expanded cross-sectional view of a part of FIG. 2. FIG. 3B is
a cross-sectional view showing a modification of the structure
shown in FIG. 3A. In the following, the invention will be described
with reference to FIGS. 1 through 3B as far as any specific
explanation is not made and the reference numbers designating the
constituent elements not illustrated in the drawings will not be
described in the drawings.
Referring now to FIGS. 1 through 3A, the pressure detecting
apparatus 100 according to the first embodiment includes a pressure
detecting device 110, a housing base 120 housing pressure detecting
device 110 therein, and a housing cover 130 mounted on housing base
120. Pressure detecting device 110, housing base 120 and housing
cover 130 are arranged in a coaxial manner with the centers thereof
aligned on a central axis C.
Pressure detecting device 110 includes a semiconductor substrate
111 made of silicon and a pedestal 112 made of glass and bonded to
semiconductor substrate 111. Semiconductor substrate 111 is bonded
to pedestal 112 by the anodic bonding technique known to those
skilled in the art to reduce the stress exerted from housing base
120. Semiconductor substrate 111 has a recess 111c in the bottom
surface 111b on the side of the bonding surface 112a of pedestal
112. Pressure detecting device 110 uses recess 111c of
semiconductor substrate 111 closed by bonding surface 112a of
pedestal 112 for a reference pressure chamber 113. Pedestal 112 is
a hexahedron made of heat-resisting glass and having rectangular
cross sections.
A diaphragm 114 is formed in the portion of pressure detecting
device 110 corresponding to reference pressure chamber 113 of
semiconductor substrate 111. Not-shown strain gauges are formed on
diaphragm 114 and a not-shown bridge circuit is formed by
connecting the strain gauges in the form of a bridge. A not shown
amplifier circuit connected to the bridge circuit is formed in
semiconductor substrate 111.
A strain is caused in pressure detecting device 110 when a pressure
is exerted to diaphragm 114 of semiconductor substrate 111. An
electrical signal is outputted from the bridge circuit in the form
of a voltage caused by the stress. The electrical signal is
amplified by the not shown amplifier circuit and the amplified
electrical signal is outputted from the amplifier circuit. Pressure
detecting device 110 that has the structure as described above and
works as described above is an absolute-pressure-type one that
employs strain gauges. Alternatively, pressure detecting device 110
may be an electrostatic-capacitance-type one.
Housing base 120 is a resin molding material made of polyphenylene
sulfide (hereinafter referred to as "PPS") and such a thermoplastic
resin. Housing base 120 includes a housing recess 121 for housing
pressure detecting device 110 therein. Housing base 120 includes
also a space on the opening side of housing recess 121. The space
on the opening side of housing recess 121 constitutes a part of the
pressure detecting chamber described later. Alternatively, housing
base 120 may be made of a heat-resisting thermoplastic resin other
than PPS with no associated problem.
Pressure detecting device 110 is housed in housing recess 121 of
housing base 120 in such a manner that pressure detecting device
110 is connected and fixed to housing recess 121 via a connecting
material 129. In detail, pressure detecting device 110 is connected
and fixed to housing base 120 with connecting material 129
interposed between the bottom surface 121a of housing recess 121
and the bottom surface 112b of pedestal 112, on which pressure
detecting device 110 is mounted. Thus, pressure detecting device
110 is fixedly supported by housing base 120.
Connecting material 129 is a resin material made of a silicone
resin adhesive and such a silicone resin. In detail, connecting
material 129 is made of a silicone resin adhesive (X32-2170AB
supplied from Shin-Etsu Chemical Co., Ltd.). Connecting material
129 exhibits a tensile elongation percentage of 400% or higher.
Connecting material 129 is formed such that the thickness thereof
(the distance between bottom surface 121a of housing recess 121 and
bottom surface 112b of pedestal 112) is from 30 .mu.m to 100
.mu.m.
Referring now to FIG. 3B, protrusions 150 maybe formed on bottom
surface 121a of housing recess 121 to adjust the thickness of
connecting material 129 with no associated problem. Protrusions 150
are formed in such an arrangement that the tips of protrusions 150
are in contact with the four corners of bottom surface 112b of
pedestal 112, to which pressure detecting device 110 is fixed.
Alternatively, protrusions 150 may be shaped with respective
protruding stripes. Protrusions 150 are from 30 .mu.m to 100 .mu.m
in height corresponding to the thickness of connecting material
129. It is not always necessary for the tips of protrusions 150 to
be in contact with bottom surface 112b of pedestal 112. In other
words, connecting material 129 may be interposed between pedestal
112 and the tip's of protrusions 150. Connecting material 129
formed as described above facilitates absorbing the thermal stress
so that the thermal stress may not be transmitted from housing base
120 to pressure detecting device 110 via connecting material 129
and effectively preventing thermal response delay from arising in
pressure detecting apparatus 100.
Lead terminals 122 are integrated into housing base 120 by
insertion molding such that lead terminals 122 are extending from
the vicinity of the opening of housing recess 121 in the direction
perpendicular to the central axis C. Lead terminals 122 are led
outside housing base 120. Each lead terminal 122 is a plate formed
by punching a base alloy of nickel (Ni) and iron (Fe). Each lead
terminal 122 includes a land section 123 arranged around the
opening of housing recess 121 and a lead section 124 extended from
land section 123 to the outside of housing base 120. As shown in
FIG. 1, eight lead sections 124 are exemplary disposed in pressure
detecting apparatus 100.
Land section 123 on each lead terminal 122 is connected
electrically, via bonding wires 125 made of aluminum (Al) or gold
(Au), to the surface 111a of semiconductor substrate 111 connected
and fixed to housing base 120. Lead section 124 of each lead
terminal 122 is connected to an external wiring material (not
shown) outside housing base 120. Although not illustrated, an
internal circuit, connected to pressure detecting device 110 or
land sections 123 of lead terminals 122 via bonding wires 125, may
be disposed in housing base 120 with no problem. The internal
circuit adjusts the electrical signals outputted from pressure
detecting device 110 and outputs the adjusted signals outside
pressure detecting apparatus 100.
In the space formed on the opening side of housing recess 121 in
housing base 120, a protecting material 126 is formed in such a
manner that protecting material 126 covers and seals the surface
111a of semiconductor substrate 111 together with bonding wires 125
and land sections 123 of lead terminals 122. Protecting material
126 is made of a gel resin. Protecting material 126 is disposed to
protect pressure detecting device 110, bonding wires 125 and such
constituent elements from contaminants and to transmit the pressure
to be measured to pressure detecting device 110 without fail. It is
preferable to dispose protecting material 126 also between the side
face of housing recess 121 and the side face of pressure detecting
device 110.
In the circumference portion of the opening side surface of housing
base 120, an insert-fitting groove 127 is formed. Housing cover 130
is mounted on housing base 120 with an insert-fitting protrusion
137 protruding from housing cover 130 made to fit into
insert-fitting groove 127. Housing cover 130 and housing base 120
are adhered and fixed to each other with a not shown adhesive
filling insert-fitting groove 127. Pressure detecting device 110
housed in housing base 120 is sealed and fixed to pressure
detecting apparatus 100 by housing cover 130.
Housing cover 130 is a resin molding made of PPS in the same manner
as housing base 120. Housing cover 130 includes a flange section
131 and a cylindrical pressure transmitting section 132 standing
vertically from the major surface 131a of flange section 131.
Housing cover 130 has a cross-sectional structure shaped with a
letter T. A pressure transmitting hole 133 is bored through
pressure transmitting section 132 concentrically with the central
axis C. When housing cover 130 is bonded and fixed to housing base
120, pressure transmitting hole 133 is connected to the space in
housing base 120. Housing cover 130 may be made of any
heat-resisting resin other than PPS with no associated problem. A
pressure detecting chamber 128 is the space in housing base 120
sectioned by flange section 131 of housing cover 130.
The pressure of the air, for example, which is a measurement
environment, is transmitted to pressure detecting chamber 128
through pressure transmitting hole 133 bored through pressure
transmitting section 132 of housing cover 130. Diaphragm 114 is
deformed by the difference between the air pressure transmitted to
pressure detecting chamber 128 and the internal pressure of
reference pressure chamber 113 in pressure detecting device 110. An
electrical signal is outputted from pressure detecting device 110
based on the strain caused by the deformation of diaphragm 114. The
electrical signal outputted from pressure detecting device 110 is
outputted outside pressure detecting apparatus 100 via bonding
wires 125, the internal circuit, and lead terminals 122. The
pressure is measured by a not shown measuring apparatus disposed
outside pressure detecting apparatus 100 based on the outputted
electrical signal.
Pressure detecting device 110 and housing base 120 are connected
and fixed to each other by connecting material 129 exhibiting a
tensile elongation percentage of about 400% or higher. Therefore,
pressure detecting apparatus 100 facilitates obtaining a structure
that transmits hardly any thermal stress caused from housing base
120 to pressure detecting device 110, thereby effectively
preventing thermal response delay from arising, and thus producing
pressure measurement results with high reproducibility.
Pressure detecting apparatus 100 as described above is manufactured
in the following way. Dies are formed to fit housing base 120 and
housing cover 130. For forming housing base 120, lead terminals 122
are fixed at the respective positions in the die for exclusive use,
and housing base 120 is formed by loading a resin such as PPS into
the die, and by cooling to solidify the resin. Housing cover 130 is
formed by loading a resin such as PPS into the die for exclusive
use and by cooling to solidify the resin. When PPS is used as the
resin for housing base 120 and housing cover 130, gases are liable
to be caused in molding PPS and flashes are liable to be caused on
the moldings. Therefore, if degassing is conducted and flashes are
removed, housing base 120 and housing cover 130 will be
manufactured very precisely.
After forming housing base 120 and housing cover 130, pressure
detecting device 110 is connected and fixed to housing recess 121
of housing base 120 via connecting material 129, the internal
circuit is mounted, and lead terminals 122 are connected to
pressure detecting device 110 and to the internal circuit via
bonding wires 125. The space on the opening side of housing recess
121 and the space between pressure detecting device 110 and housing
recess 121 are covered with protecting material 126 made of a gel
resin. And, housing cover 130 is mounted on and fixed to housing
base 120. Thus, pressure detecting apparatus 100 is
manufactured.
Pressure detecting apparatus 100, which connects and fixes pressure
detecting device 110 to housing base 120 with connecting material
129 exhibiting a tensile elongation percentage of about 400% or
higher, realizes a structure that transmits hardly any thermal
stress caused from housing base 120 to pressure detecting device
110. The reasons for defining the tensile elongation percentage of
connecting material 129 as described above will be explained
below.
FIG. 4 shows a curve relating the output variation (%F.S..times.10)
caused by the thermal response shift with the tensile elongation
percentage (%) of connecting material 129. The present inventors
have conducted the following tests for defining the tensile
elongation percentage of connecting material 129. A strength
characteristics measuring apparatus (EZ Test supplied from Shimadzu
Corp.) is used for measuring the tensile elongation percentage.
Tensile elongation percentage measuring tests are conducted on a
silicone resin adhesive (X32-2170AB supplied from Shin-EtsuChemical
Co., Ltd.) (hereinafter referred to as a "sample 1") and a silicone
resin adhesive (TSE322 supplied from GE Toshiba Silicones Co.,
Ltd.) for comparison (hereinafter referred to as a "sample 2").
The samples 1 and 2 are 8 mm in width, 1.5 mm in height (thickness)
and 50 mm in length. The distance between the jigs for fixing the
sample to the measuring apparatus is set at 10 mm. The tensile
tests are conducted at the pulling rate of 60 mm/min. The output
variation caused by the thermal response shift and described in
FIG. 4 is the shift value of an output from the pressure detecting
apparatus (detected output variation) caused when the pressure
detecting apparatus, left in an environment of 130.degree. C. for 1
hr, is returned to the room temperature environment (from
20.degree. C. to 25.degree. C.). The unit of the output variation
caused by the thermal response shift is the percentage of an output
voltage from pressure detecting apparatus 100 to the full scale
(hereinafter referred to as the "F.S.") of the output. Since the
output voltage values obtained are so small that the output voltage
values are multiplied by 10 and the corrected output voltage values
are expressed.
Since it is necessary for pressure detecting apparatus 100 and such
on-vehicle equipment to be very precise, it is preferable for the
output variation caused by the thermal response shift to be 0.125
(%F.S.) or less or 1.25 (%F.S..times.10) or less in the 10 times
expression. The tests are conducted based on the threshold for
judging the output variations caused by the thermal response shift
set at 1.25 (%F.S..times.10). The elongation of connecting material
129 is the difference obtained by setting two gage marks (fixed
points fixed by the fixing jigs), by measuring the distance L0
between the gage marks (the distance between the fixing jigs), by
measuring the distance L1 between the gage marks after the tests,
and by calculating L1 L0. The elongation percentage in % is
calculated from the following formula (1). 100.times.(L1-L0)/L0
(1)
The tensile elongation percentage measuring tests conducted under
the conditions as described above have revealed clear differences
expressed by a correlation curve 401 shown in FIG. 4 that connects
the measurement results on the samples 1 and 2. Correlation curve
401 represents the correlation between the output variations and
the elongation percentage in the measurement results on the samples
1 and 2. Correlation curve 401 indicates that as the elongation
percentage becomes larger, the output variation becomes smaller,
resulting in an improved thermal response. The lower right end
point 402 on correlation curve 401 represents the results on the
sample 1 and the upper left endpoint 403 on correlation curve 401
represents the results on the sample 2.
In the sample 1, when the tensile elongation percentage is around
500%, the output variation caused by the thermal response shift is
about 0.77 (%F.S..times.10) as correlation curve 401 clearly
indicates. In the sample 2, when the tensile elongation percentage
is around 200%, the output variation caused by the thermal response
shift is about 3.6 (%F.S..times.10) as correlation curve 401
clearly indicates. For conducting the tests, the hardness (JIS A)
is set at 20 for the sample 1 and at 17 for the sample 2. It has
been clarified that if connecting material 129 is made of a
material having a hardness of around 20, there will exist almost no
correlation between the output variation caused by the thermal
response shift and the hardness. Therefore, if connecting material
129 is made of a material having a hardness of around 20, the
correlation between the elongation characteristics of connecting
material 129 and the output variation caused by the thermal
response shift will be large. In other words, if connecting
material 129 is made of a material having a hardness of around 20,
there will be almost no correlation between the elongation
percentage and the hardness.
Therefore, if the elongation percentage of connecting material 129
is set to be in the range indicated by the black arrows in FIG. 4
(the range, in which the output variation is 1.25 (%F.S..times.10)
or smaller and the elongation percentage is about 400% or higher),
connecting material 129 will absorb the stress exerted from housing
base 120 to pressure detecting device 110 by the excellent
elongation characteristics thereof and pressure detecting apparatus
100 will be provided with excellent thermal response.
As described above in connection with the embodiments of the
invention, connecting material 129 exhibiting excellent elongation
characteristics absorbs the stress exerted from housing base 120 so
that the stress may not be transmitted to pressure detecting device
110. Therefore, pressure detecting apparatus 100 exhibits very
precise initial detection performances and guarantees very reliable
pressure detection performances.
Although the materials and the shapes of housing base 120 and
housing cover 130 and the structures of the constituent elements in
pressure detecting apparatus 100 have been described numerically,
the descriptions are exemplary and changes and modifications are
obvious to those skilled in the art without departing from the true
spirit of the invention.
As described above, since pressure detecting device 110 and housing
base 120 are connected and fixed to each other with connecting
material 129 exhibiting an elongation percentage of about 400% or
higher, pressure detecting apparatus 100 according to the invention
facilitates absorbing the exerted stress based on the excellent
elongation characteristics thereof and exhibits excellent thermal
response. Pressure detecting apparatus 100 that exhibits excellent
thermal response facilitates realizing a structure immune to the
temperature change caused in the measurement environment and
obtaining measurement results with very high reproducibility.
As described above, the pressure detecting apparatus according to
the invention is employable for various kinds of use, in which
pressure detection or pressure measurement is conducted.
The disclosure of Japanese Patent Application No. 2005-130533 filed
on Apr. 27, 2005, is incorporated herein.
* * * * *